[M-IS32_30PM2] 地球掘削科学

[MIS32-22] 科学掘削泥水検層：第一期IODPでの成果

*杉原 孝充¹、青池 寛¹、モー キョースー¹ (1.海洋研究開発機構　地球深部探査センター)

キーワード：地球深部探査船　ちきゅう, 統合国際掘削計画, 泥水検層, カッティングス, 泥水ガスモニタリング, 科学掘削

Mud logging has been a key technology for scientific drilling operation by D/V Chikyu. In order to penetrate into deeper formation by riser drilling, full-coring operation to targeted total depth is difficult due to taking much operation time. Therefore mud logging obviously contributes to acquiring continuous geological and geochemical data from formation and circulating fluid in formation to targeted total depth. In the IODP 1st phase, riser drilling operations with mud logging were conducted 4 times by the Chikyu (Expeditions 319, 337, 338, and 348). In this paper, we highlight some results of mud logging operated in the past operation and discuss on technical challenging for future riser operations by the Chikyu.Mud logging is roughly composed of three components, lithological logging on cuttings, mud gas monitoring, and mud circulation/drilling parameters monitoring. As well known, cuttings lithology logging and mud gas monitoring are important tool to understand geological characteristics beneath drilling site based on results of not only the IODP riser operations by the Chikyu but also ICDP onshore drilling projects (e.g., Unzen and SAFOD). However, potential of mud circulation and drilling parameters monitoring associated with cuttings and mud gas analyses has not been discussed in detail in scientific drilling community. d-exponent is an indicator to detect zone of high pore pressure during drilling and it is well developed in the petroleum industry. d-exponent is defined as normalized rate of penetration (ROP) with rotation speed (RPM) and weight on bit (WOB), and in general case, d-exponent gradually decreases as entering into high pore pressure zone increasing ROP. During Expedition 348, we often faced formation with difficulty of drilling, and supposed there was relatively higher pore pressure zone based on the d-exponent analysis. In this presentation, we will discuss on comprehensive mud logging data analysis including data of d-exponent acquired in the past riser drilling operation and assess its potential for future expeditions.